Optical image measurement device

ABSTRACT

A fundus oculi observation device acts as an optical image measurement device capable of measuring an OCT image such as a tomographic image of a fundus oculi, or the like, and is configured so as to calculate the signal level of the formed OCT image, determine whether the signal level exceeds a threshold value, and change the position of a reference mirror so that the signal level is determined to exceed the threshold value.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical image measurement deviceconfigured to apply a light beam to a measurement subject and form animage of the surface morphology or internal morphology of themeasurement subject by using a reflected light or a transmitted light.

2. Description of the Related Art

In recent years, attention has been focused on an optical imagemeasurement technology of forming an image showing the surfacemorphology or internal morphology of a measurement subject by using alight beam from a laser light source or the like. Because this opticalimage measurement technology does not have invasiveness to human bodiesunlike an X-ray CT device, it is particularly expected to further usethis technology in the medical field.

Japanese Unexamined Patent Application Publication JP-A 11-325849discloses an optical image measurement device having a configurationthat: a measuring arm scans an object through a rotary deflection mirror(Galvano mirror); a reference mirror is disposed to a reference arm; aninterferometer is used at the outlet so that the intensity of lightappearing from interference of light fluxes from the measuring arm andthe reference arm is analyzed by a spectrometer; and a device graduallychanging the light flux phase of the reference light in non-continuousvalues is disposed to the reference arm.

The optical image measurement device of JP-A 11-325849 uses a method ofso-called “Fourier Domain Optical Coherence Tomography (OCT)” based ontechnology of German Patent Application Publication DE4309056A1. That isto say, a beam of a low-coherence light is applied to a measurementsubject, the spectrum intensity distribution of a reflected light isobtained, and the obtained distribution is subjected to Fouriertransformation, whereby an image of the morphology of the measurementsubject in a depth direction (z-direction) is formed.

Furthermore, the optical image measurement device described in JP-A11-325849 is provided with a Galvano mirror that scans with an opticalbeam (signal light), whereby it is possible to form an image of adesired measurement region of a measurement subject. Because thisoptical image measurement device is configured to scan with a light beamonly in one direction (x-direction) orthogonal to the z-direction, aformed image is a 2-dimensional cross-sectional image of the depthdirection (z-direction) along the light beam scanning direction(x-direction).

Besides, Japanese Unexamined Patent Application Publication JP-A2003-543 discloses a configuration in which the aforementioned opticalimage measurement device is applied to the field of ophthalmology.

An optical image measurement device forms an image by measuring a depthalmost the same as the length of a reference arm (the optical pathlength of a reference light). Therefore, in order to capture an image ofa desired depth position, it is necessary to place a reference mirror ata position corresponding to the depth position. Considering the use of alow-coherence light, alignment of the reference mirror, namely,alignment of the measurement position in the depth direction must beconducted precisely.

Further, in an optical image measurement device, the measurementsensitivity is the most favorable at a depth position that coincideswith the optical path length of the reference light (origin of thez-direction), and the measurement sensitivity becomes lower as it isdistant from the origin. Also from this aspect, it is understood thatalignment of the measurement position in the depth direction needsprecision.

However, the conventional optical image measurement devices have aproblem in that it is impossible to easily align the measurementposition in the depth direction of a measurement subject.

SUMMARY OF THE INVENTION

The present invention has been devised to solve the problem as describedabove, and an object of the present invention is to provide an opticalimage measurement device capable of easily aligning a measurementposition in the depth direction of a measurement subject.

In a first aspect of the present invention, an optical image measurementdevice comprises: a light source configured to emit a low-coherencelight; an interference-light generator configured to generate aninterference light by splitting the emitted low-coherence light into asignal light heading toward a measurement subject and a reference lightheading toward a reference object, and superimposing the signal lightpassed through the measurement subject and the reference light passedthrough the reference object; a changer configured to change adifference in optical path length between the signal light and thereference light; a detector configured to detect the generatedinterference light; an image forming part configured to form an imagebased on the result of the detection by the detector; an analyzerconfigured to analyze the formed image to calculate a signal level or aratio of a signal level and a noise level of an image, and determinewhether the signal level or the ratio of the signal level and the noiselevel exceeds a threshold value; and a controller configured to controlthe changer to change the difference in optical path length so that theanalyzer determines the difference to exceed the threshold value.

In a second aspect of the present invention, an optical imagemeasurement device comprises: a light source configured to emit alow-coherence light; an interference-light generator configured togenerate a interference light by splitting the emitted low-coherencelight into a signal light heading toward a measurement subject and areference light heading toward a reference object, and superimposing thesignal light passed through the measurement subject and the referencelight passed through the reference object; a changer configured tochange a difference in optical path length between the signal light andthe reference light; a detector configured to detect the generatedinterference light; an image forming part configured to form an imagewithin a predetermined frame based on the result of the detection by thedetector; and a controller configured to control the changer to changethe difference in optical path length so that a partial imagecorresponding to a predetermined depth position of the measurementsubject in the formed image is placed in a specific position within thepredetermined frame.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic configuration diagram showing one example of theentire configuration in a preferred embodiment of a device related tothe present invention.

FIG. 2 is a schematic configuration diagram showing one example of theconfiguration of a scan unit installed in a retinal camera unit in thepreferred embodiment of the device related to the present invention.

FIG. 3 is a schematic configuration diagram showing one example of theconfiguration of an OCT unit in the preferred embodiment of the devicerelated to the present invention.

FIG. 4 is a schematic block diagram showing one example of the hardwareconfiguration of an arithmetic control unit in the preferred embodimentof the device related to the present invention.

FIG. 5 is a schematic block diagram showing one example of theconfiguration of a control system in the preferred embodiment of thedevice related to the present invention.

FIG. 6 is a schematic view showing one example of the appearance of anoperation panel in the preferred embodiment of the device related to thepresent invention.

FIG. 7 is a schematic block diagram showing one example of thefunctional configuration of the arithmetic control unit in the preferredembodiment of the device related to the present invention.

FIGS. 8A and 8B are schematic views showing one example of a scanningpattern of a signal light in the preferred embodiment of the devicerelated to the present invention. FIG. 8A shows one example of ascanning pattern of the signal light when a fundus oculi is seen fromthe incident side of the signal light to an eye. FIG. 8B shows oneexample of an arrangement pattern of scanning points on each scanningline.

FIG. 9 is a schematic view showing one example of a scanning pattern ofthe signal light and a pattern of a tomographic image formed along eachscanning line in the preferred embodiment of the device related to thepresent invention.

FIG. 10 is a flowchart showing one example of a usage pattern in thepreferred embodiment of the device related to the present invention.

FIG. 11 is a schematic explanation view for explaining a specificexample of the usage pattern in the preferred embodiment of the devicerelated to the present invention.

FIG. 12 is a schematic explanation view for explaining a specificexample of the usage pattern in the preferred embodiment of the devicerelated to the present invention.

FIG. 13 is a schematic explanation view for explaining a specificexample of the usage pattern in the preferred embodiment of the devicerelated to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

One example of a preferred embodiment of an optical image measurementdevice according to the present invention will be described in detailreferring to the drawings.

[Configuration of Device]

First, referring to FIGS. 1 through 7, the configuration of the opticalimage measurement device according to a first embodiment of the presentinvention will be described. FIG. 1 shows one example of the entireconfiguration of a fundus oculi observation device 1 having a functionas the optical image measurement device according to this embodiment.FIG. 2 shows one example of the configuration of a scan unit 141 in aretinal camera unit 1A. FIG. 3 shows one example of the configuration ofan OCT unit 150. FIG. 4 shows one example of the hardware configurationof an arithmetic control unit 200. FIG. 5 shows one example of theconfiguration of a control system of the fundus oculi observation device1. FIG. 6 shows one example of the configuration of an operation panel 3a disposed to the retinal camera unit 1A. FIG. 7 shows one example ofthe configuration of a control system of the arithmetic control unit200.

[Entire Configuration]

The fundus oculi observation device 1 related to this embodimentcomprises a retinal camera unit 1A, an OCT unit 150, and an arithmeticcontrol unit 200 as shown in FIG. 1. The retinal camera unit 1A hasalmost the same optical system as the conventional retinal cameras forphotographing 2-dimensional images of the fundus oculi surface. The OCTunit 150 houses an optical system that functions as an optical imagemeasurement device. The arithmetic control unit 200 is equipped with acomputer for executing various types of arithmetic processes, controlprocesses, or the like.

To the OCT unit 150, one end of a connection line 152 is attached. Aconnector part 151 for connecting the connection line 152 to the retinalcamera unit 1A is attached to the other end of the connection line 152.A conductive optical fiber runs through inside the connection line 152.Thus, the OCT unit 150 and the retinal camera unit 1A are opticallyconnected via the connection line 152.

Configuration of Retinal Camera Unit

The retinal camera unit 1A is used for forming a 2-dimensional image ofthe surface of a fundus oculi of an eye, based on optically obtaineddata (data detected by the imaging devices 10 and 12). Herein, the“2-dimensional image of the surface of the fundus oculi” refers to acolor or monochrome image of the surface of the fundus oculi having beenphotographed, a fluorescent image (a fluorescein angiography image, anindocyanine green fluorescent image, etc.), and the like. As well as theconventional retinal camera, the retinal camera unit 1A is provided withan illumination optical system 100 that illuminates a fundus oculi Ef ofan eye E, and an imaging optical system 120 that guides the fundus oculireflection light of the illumination light to the imaging device 10.

Although the details will be described later, the imaging device 10 inthe imaging optical system 120 of this embodiment detects theillumination light having a wavelength in the near-infrared region.Moreover, this imaging optical system 120 is further provided with theimaging device 12 for detecting the illumination light having awavelength in the visible region. Moreover, this imaging optical system120 guides a signal light coming from the OCT unit 150 to the fundusoculi Ef, and guides the signal light passed through the fundus oculi Efto the OCT unit 150.

The illumination optical system 100 comprises: an observation lightsource 101; a condenser lens 102; an imaging light source 103; acondenser lens 104; exciter filters 105 and 106; a ring transparentplate 107; a mirror 108; an LCD (Liquid Crystal Display) 109; anillumination diaphragm 110; a relay lens 111; an aperture mirror 112;and an objective lens 113.

The observation light source 101 emits an illumination light having awavelength of the visible region included in a range of, for example,about 400 nm thorough 700 nm. Moreover, the imaging light source 103emits an illumination light having a wavelength of the near-infraredregion included in a range of, for example, about 700 nm through 800 nm.The near-infrared light emitted from this imaging light source 103 isset so as to have a shorter wavelength than the light used by the OCTunit 150 (described later).

Further, the imaging optical system 120 comprises: an objective lens113; an aperture mirror 112 (an aperture 112 a thereof); an imagingdiaphragm 121; barrier filters 122 and 123; a variable magnifying lens124; a relay lens 125; an imaging lens 126; a dichroic mirror 134; afield lens 128; a half minor 135; a relay lens 131; a dichroic minor136; an imaging lens 133; the imaging device 10 (image pick-up element10 a); a reflection mirror 137; an imaging lens 138; the imaging device12 (image pick-up element 12 a); a lens 139; and an LCD 140.

The dichroic mirror 134 is configured to reflect the fundus oculireflection light (having a wavelength included in a range of about 400nm through 800 nm) of the illumination light from the illuminationoptical system 100, and transmit a signal light LS (having a wavelengthincluded in a range of, for example, about 800 nm through 900 nm;described later) from the OCT unit 150.

Further, the dichroic mirror 136 is configured to transmit theillumination light having a wavelength of the visible region from theillumination optical system 100 (a visible light having a wavelength ofabout 400 nm through 700 nm emitted from the observation light source101), and reflect the illumination light having a wavelength of thenear-infrared region (a near-infrared light having a wavelength of about700 nm through 800 nm emitted from the imaging light source 103).

On the LCD 140, a fixation target (internal fixation target) or the likefor fixing the eye E is displayed. The light from this LCD 140 isreflected by the half mirror 135 after being converged by the lens 139,and is reflected by the dichroic mirror 136 through the field lens 128.Then, the light passes through the imaging lens 126, the relay lens 125,the variable magnifying lens 124, the aperture mirror 112 (aperture 112a thereof), the objective lens 113 and the like, and enters the eye E.Consequently, an internal fixation target or the like is projected inthe fundus oculi Ef of the eye E.

The image pick-up element 10 a is an image pick-up element such as a CCD(Charge Coupled Device) and a CMOS (Complementary metal OxideSemiconductor) installed in the imaging device 10 such as a TV camera,and is particularly used for detecting light having a wavelength of thenear-infrared region. In other words, the imaging device 10 is aninfrared TV camera for detecting near-infrared light. The imaging device10 outputs video signals as a result of detection of the near-infraredlight.

A touch panel monitor 11 displays a 2-dimensional image (a fundus oculiimage Ef′) of the surface of the fundus oculi Ef, based on the videosignals. The video signals are sent to the arithmetic control unit 200,and the fundus oculi image is displayed on the display (describedlater).

At the time of imaging of the fundus oculi by the imaging device 10, forexample, the illumination light emitted from the imaging light source103 of the illumination optical system 100 and having a wavelength ofthe near-infrared region is used.

On the other hand, the image pick-up element 12 a is an image pick-upelement such as a CCD and a CMOS installed in the imaging device 12 suchas a TV camera, and is particularly used for detecting light having awavelength of the visible region (that is, the imaging device 12 is a TVcamera for detecting visible light). The imaging device 12 outputs videosignals as a result of detection of the visible light.

The touch panel monitor 11 displays a 2-dimensional image (fundus oculiimage Ef′) of the surface of the fundus oculi Ef, based on the videosignals. The video signals are sent to the arithmetic control unit 200,and the fundus oculi image Ef′ is displayed on the display (describedlater).

At the time of imaging of the fundus oculi by the imaging device 12, forexample, the illumination light emitted from the observation lightsource 101 of the illumination optical system 100 and having awavelength of the visible region is used.

The retinal camera unit 1A is provided with a scan unit 141 and a lens142. The scan unit 141 includes a component for scanning at anapplication position of the fundus oculi Ef with light emitted from theOCT unit (signal light LS; described later).

The lens 142 makes the signal light LS guided from the OCT unit 150through the connection line 152 enter the scan unit 141 in the form of aparallel light flux. Moreover, the lens 142 acts so as to converge thefundus oculi reflection light of the signal light LS passed through thescan unit 141.

FIG. 2 shows one example of a specific configuration of the scan unit141.

The scan unit 141 comprises Galvano mirrors 141A and 141B, andreflection mirrors 141C and 141D.

The Galvano mirrors 141A and 141B are reflection mirrors disposed so asto be rotatable about rotary shafts 141 a and 141 b, respectively. TheGalvano mirrors 141A and 141B are rotated about the rotary shafts 141 aand 141 b, respectively, by a drive mechanism described later (mirrordrive mechanisms 241 and 242 shown in FIG. 5), whereby the orientationsof reflection surfaces thereof (faces reflecting the signal light LS),namely, the positions of the Galvano mirrors 141A and 141B are changed,respectively.

The rotary shafts 141 a and 141 b are arranged so as to be orthogonal toeach other. In FIG. 2, the rotary shaft 141 a of the Galvano mirror 141Ais arranged in parallel to the paper face of FIG. 2, whereas the rotaryshaft 141 b of the Galvano mirror 141B is arranged so as to beorthogonal to the paper face of FIG. 2.

That is to say, the Galvano mirror 141B is formed so as to be rotatablein the directions indicated by an arrow pointing in both directions inFIG. 2, whereas the Galvano mirror 141A is formed so as to be rotatablein the directions orthogonal to the arrow pointing in both thedirections. Consequently, the pair of Galvano mirrors 141A and 141B actso as to change the reflecting directions of the signal light LS todirections orthogonal to each other. As seen from FIGS. 1 and 2, scanwith the signal light LS is performed in the x direction when theGalvano mirror 141A is rotated, and scan with the signal light LS isperformed in the y direction when the Galvano mirror 141B is rotated.

The signal lights LS reflected by the Galvano mirrors 141A and 141B arereflected by reflection mirrors 141C and 141D, thereby traveling in thesame directions as having entered into the Galvano mirror 141A.

As described before, the conductive optical fiber 152 a runs through theinside of the connection line 152, and an end face 152 b of the opticalfiber 152 a is arranged facing the lens 142. The signal light LS emittedfrom this end face 152 b travels while expanding its beam diametertoward the lens 142. The light is converged into a parallel light fluxby this lens 142. On the contrary, the signal light LS passed throughthe fundus oculi Ef is converged toward the end face 152 b by the lens142, and guided to the optical fiber 152 a.

Configuration of OCT Unit

Next, the configuration of the OCT unit 150 will be described referringto FIG. 3. The OCT unit 150 is a device configured to form a tomographicimage of the fundus oculi based on optically obtained data (datadetected by a CCD 184 described later).

The OCT unit 150 has almost the same optical system as the conventionaloptical image measurement device. That is, the OCT unit 150 has: aninterferometer that splits the light emitted from the light source intoa reference light and a signal light and generates interference-light bysuperposing the reference light passed through a reference object andthe signal light passed through a measurement object (fundus oculi Ef);and a part configured to detect this interference-light and outputsignals as the result of the detection (detection signals) toward thearithmetic control unit 200. The arithmetic control unit 200 forms atomographic image of the measurement object (fundus oculi Ef), byanalyzing the detection signals.

A low-coherence light source 160 is composed of a broadband lightsource, such as a super luminescent diode (SLD) and a light emittingdiode (LED), configured to emit a low-coherence light L0. Thislow-coherence light L0 is, for example, a light that has a wavelength ofthe near-infrared region and has a time-wise coherence length ofapproximately several tens of micrometers. The low-coherence lightsource 160 corresponds to one example of the “light source” of thepresent invention.

The low-coherence light L0 has a longer wavelength than the illuminationlight (wavelength: about 400 nm through 800 nm) of the retinal cameraunit 1A, for example, a wavelength included in a range of about 800 nmthrough 900 nm.

The low-coherence light L0 emitted from the low-coherence light source160 is guided to an optical coupler 162 through an optical fiber 161.The optical fiber 161 is composed of, for example, a single mode fiberor a PM (Polarization maintaining) fiber. The optical coupler 162 splitsthis low-coherence light L0 into a reference light LR and the signallight LS.

Although the optical coupler 162 acts as both a part (splitter) forsplitting light and a part (coupler) for superposing lights, it will beherein referred to as an “optical coupler” idiomatically.

The reference light LR generated by the optical coupler 162 is guided byan optical fiber 163 composed of a single mode fiber or the like, andemitted from the end face of the fiber. The emitted reference light LRis converged into a parallel light flux by a collimator lens 171, passedthrough a glass block 172 and a density filter 173, and then reflectedby a reference mirror 174 (reference object).

The reference light LR reflected by the reference mirror 174 isconverged to the fiber end face of the optical fiber 163 by thecollimator lens 171 again through the density filter 173 and the glassblock 172. The converged reference light LR is guided to the opticalcoupler 162 through the optical fiber 163.

The glass block 172 and the density filter 173 act as a delaying partfor making the optical path lengths (optical distances) of the referencelight LR and the signal light LS coincide, and also as a dispersioncorrection part for making the dispersion characteristics of thereference light LR and the signal light LS coincide.

Further, the density filter 173 also acts as a dark filter for reducingthe amount of the reference light, and is composed of a rotating ND(neutral density) filter, for example. This density filter 173 acts soas to change the reduction amount of the reference light LR by beingrotary driven by a drive mechanism including a drive unit such as amotor (a density filter drive mechanism 244 described later; refer toFIG. 5). Consequently, it is possible to change the amount of thereference light LR contributing to generation of the interference-lightLC.

Further, the reference mirror 174 is configured so as to move in thetraveling direction (the direction of the arrow pointing both sidesshown in FIG. 3) of the reference light LR. With this configuration, itis possible to ensure the optical path length of the reference light LRaccording to the axial length of the eye E, etc. Moreover, it ispossible to capture an image of any depth position of the fundus oculiEf, by moving the reference mirror 174. The reference mirror 174 ismoved by a drive mechanism (a reference mirror driving mechanism 243described later; refer to FIG. 5) including a driver such as a motor.

On the other hand, the signal light LS generated by the optical coupler162 is guided to the end of the connection line 152 through an opticalfiber 164 composed of a single mode fiber or the like. The conductiveoptical fiber 152 a runs inside the connection line 152. Herein, theoptical fiber 164 and the optical fiber 152 a may be composed of asingle optical fiber, or may be jointly formed by connecting the endfaces of the respective fibers. In either case, it is sufficient as faras the optical fiber 164 and 152 a are configured to be capable oftransferring the signal light LS between the retinal camera unit 1A andthe OCT unit 150.

The signal light LS is guided through the inside of the connection line152 and led to the retinal camera unit 1A. Then, the signal light LSenters into the eye E through the lens 142, the scan unit 141, thedichroic mirror 134, the imaging lens 126, the relay lens 125, thevariable magnifying lens 124, the imaging diaphragm 121, the aperture112 a of the aperture mirror 112, and the objective lens 113. Thebarrier filter 122 and 123 are retracted from the optical path inadvance, respectively, when the signal light LS is made to enter the eyeE.

The signal light LS having entered the eye E forms an image on thefundus oculi (retina) Ef and is then reflected. At this moment, thesignal light LS is not only reflected on the surface of the fundus oculiEf, but also scattered at the refractive index boundary after reachingthe deep area of the fundus oculi Ef. As a result, the signal light LSpassed through the fundus oculi Ef is a light containing informationreflecting the state of the surface of the fundus oculi Ef andinformation reflecting the state of backscatter at the refractive indexboundary of the deep area tissue of the fundus oculi Ef. This light maybe simply referred to as “fundus oculi reflection light of the signallight LS.”

The fundus oculi reflection light of the signal light LS travelsreversely on the above path within the retinal camera unit 1A, and isconverged at the end face 152 b of the optical fiber 152 a. Then, thesignal light LS enters into the OCT unit 150 through the optical fiber152 a, and returns to the optical coupler 162 through the optical fiber164.

The optical coupler 162 superimposes the signal light LS returningthrough the fundus oculi Ef and the reference light LR reflected by thereference mirror 174, thereby generating the interference-light LC. Thegenerated interference-light LC is guided into a spectrometer 180through an optical fiber 165 composed of a single mode fiber or thelike.

Herein, although a Michelson-type interferometer is adopted in thisembodiment, for instance, a Mach Zender type, etc. and any type ofinterferometer may be adopted appropriately. The “interference-lightgenerator” related to the present invention comprises, for example, anoptical coupler 162, optical members on the optical path of the signallight LS (i.e., optical members placed between the optical coupler 162and the fundus oculi Ef), and optical members on the optical path of thereference light LR (i.e., optical members placed between the opticalcoupler 162 and the reference mirror 174), and specifically, comprisesan interferometer equipped with the optical coupler 162, the opticalfibers 163, 164, and the reference mirror 174.

The spectrometer 180 comprises a collimator lens 181, a diffractiongrating 182, an image-forming lens 183, and a CCD 184. The diffractiongrating 182 in this embodiment is a transmission-type diffractiongrating that transmits light; however, needless to say, areflection-type diffraction grating that reflects light may also beused. Moreover, needless to say, it is also possible to adopt, in placeof the CCD 184, other photo-detecting elements.

The interference light LC having entered the spectrometer 180 is split(resolved into spectra) by the diffraction grating 182 after convergedinto a parallel light flux by the collimator lens 181. The splitinterference light LC forms an image on the image pick-up surface of theCCD 184 by the image-forming lens 183. The CCD 184 detects therespective spectra of the interference light LC and converts toelectrical signals, and outputs the detection signals to the arithmeticcontrol unit 200. The CCD 184 functions as the “detector” of the presentinvention.

Configuration of Arithmetic Control Unit

Next, the configuration of the arithmetic control unit 200 will bedescribed. The arithmetic control unit 200 performs a process ofanalyzing detection signals inputted from the CCD 184 of thespectrometer 180 of the OCT unit 150 and forming a tomographic image ofthe fundus oculi Ef of the eye E. The analysis method is the same as theconventional technique of Fourier Domain OCT.

Further, the arithmetic control unit 200 performs a process of forming(image data of) a 2-dimensional image showing the state of the surface(retina) of the fundus oculi Ef, based on the video signals outputtedfrom the imaging devices 10 and 12 of the retinal camera unit 1A.

Furthermore, the arithmetic control unit 200 executes control of eachpart of the retinal camera unit 1A and the OCT unit 150.

The arithmetic control unit 200 executes as control of the retinalcamera unit 1A, for example: control of emission of illumination lightby the observation light source 101 or the imaging light source 103;control of insertion/retraction operations of the exciter filters 105and 106 or the barrier filters 122 and 123 to/from the optical path;control of the operation of a display device such as the LCD 140;control of shift of the illumination diaphragm 110 (control of thediaphragm value); control of the diaphragm value of the imagingdiaphragm 121; and control of shift of the variable magnifying lens 124(control of the magnification). Moreover, the arithmetic control unit200 executes control of the operation of the Galvano mirrors 141A and141B inside the scan unit 141 (operation of changing the directions ofthe reflection faces).

Further, the arithmetic control unit 200 executes as control of the OCTunit 150, for example: control of emission of the low-coherence light L0by the low-coherence light source 160; control of shift of the referencemirror 174; control of the rotary operation of the density filter 173(operation of changing the reduction amount of the reference light LR);and control of the accumulated time of the CCD 184.

One example of the hardware configuration of the arithmetic and controlunit 200 that acts as described above will be described referring toFIG. 4.

The arithmetic and control unit 200 is provided with the same hardwareconfiguration as that of a conventional computer. To be specific, thearithmetic and control unit 200 comprises: a microprocessor 201 (CPU,MPU, etc.), a RAM202, a ROM203, a hard disk drive (HDD) 204, a keyboard205, a mouse 206, a display 207, an image forming board 208, and acommunication interface (I/F) 209. These parts are connected via a bus200 a.

The microprocessor 201 comprises a CPU (Central Processing Unit), an MPU(Micro Processing Unit) or the like, and executes operationscharacteristic to this embodiment, by loading a control program 204 astored in the hard disk drive 204, onto the RAM 202.

Further, the microprocessor 201 executes control of each part of thedevice described above, various arithmetic processes, etc. Moreover, themicroprocessor 201 executes control of each part of the devicecorresponding to an operation signal from the keyboard 205 or the mouse206, control of a display process by the display 207, and control of atransmission/reception process of various data, control signals and soon by the communication interface 209.

The keyboard 205, the mouse 206 and the display 207 are used as userinterfaces in the fundus oculi observation device 1. The keyboard 205 isused as, for example, a device for typing letters, figures, etc. Themouse 206 is used as a device for performing various input operations tothe display screen of the display 207.

Further, the display 207 is any display device composed of an LCD, a CRT(Cathode Ray Tube) display or the like. The display 207 displays variousimages of the fundus oculi Ef formed by the fundus oculi observationdevice 1, and displays various screens such as an operation screen and aset-up screen.

The user interface of the fundus oculi observation device 1 is notlimited to the above configuration, and may be configured by using anyuser interface having a function of displaying and outputting variousinformation, and a function of inputting various information andoperating the device, such as a track ball, a control lever, a touchpanel type of LCD, and a control panel for ophthalmology examinations.

The image forming board 208 is a dedicated electronic circuit for aprocess of forming (image data of) images of the fundus oculi Ef of theeye E. This image forming board 208 is provided with a fundus oculiimage forming board 208 a and an OCT-image forming board 208 b.

The fundus oculi image forming board 208 a is a dedicated electroniccircuit that operates to form image data of fundus oculi images based onthe video signals from the imaging device 10 and the imaging device 12of the retinal camera unit 1A.

Further, the OCT-image forming board 208 b is a dedicated electroniccircuit that operates to form image data of tomographic images of thefundus oculi Ef, based on the detection signals from the CCD 184 of thespectrometer 180 in the OCT unit 150.

By providing the image forming board 208, it is possible to increase theprocessing speed for forming image data of fundus oculi images andtomographic images.

The communication interface 209 performs a process of sending controlsignals from the microprocessor 201, to the retinal camera unit 1A orthe OCT unit 150. Moreover, the communication interface 209 performs aprocess of receiving video signals from the imaging devices 10 and 12 ofthe retinal camera unit 1A and detection signals from the CCD 184 of theOCT unit 150, and inputting the signals to the image forming board 208.At this time, the communication interface 209 operates to input thevideo signals from the imaging devices 10 and 12, to the fundus oculiimage forming board 208 a, and input the detection signal from the CCD184, to the OCT-image forming board 208 b.

Further, in a case where the arithmetic and control unit 200 isconnected to a network such as a LAN (Local Area Network) and theInternet, it is possible to configure so as to be capable of datacommunication via the network, by providing the communication interface209 with a network adapter like a LAN card or communication equipmentlike a modem. In this case, by mounting a server accommodating thecontrol program 204 a on the network, and at the same time, configuringthe arithmetic and control unit 200 as a client terminal of the server,it is possible to cause the fundus oculi observation device 1 to executethe operation according to the present invention.

Configuration of Control System

Next, the configuration of the control system of the fundus oculiobservation device 1 will be described referring to FIG. 5 through FIG.7. FIG. 5 is a block diagram showing a part related to the operationsand processes according to the present invention particularly selectedfrom among constituents composing the fundus oculi observation device 1.FIG. 6 shows one example of the configuration of the operation panel 3 adisposed to the retinal camera unit 1A. FIG. 7 is a block diagramshowing a detailed configuration of the arithmetic and control unit 200.

(Controller)

The control system of the fundus oculi observation device 1 isconfigured mainly having a controller 210 of the arithmetic and controlunit 200 shown in FIG. 5. The controller 210 comprises themicroprocessor 201, the RAM202, the ROM203, the hard disk drive 204(control program 204 a), and the communication interface 209.

The controller 210 executes the aforementioned controlling processesthrough the microprocessor 201 operating based on the control program204 a. In specific, for the retinal camera unit 1A, the controller 210performs control of the mirror drive mechanisms 241 and 242 for changingthe positions of the Galvano mirrors 141A and 141B, control of thedisplay operation of the internal fixation target by the LCD 140, etc.

Further, for the OCT unit 150, the controller 210 performs control ofthe low-coherence light source 160 and the CCD 184, control of thedensity filter drive mechanism 244 for rotating the density filter 173,control of the reference-mirror driving mechanism 243 for moving thereference mirror 174 in the traveling direction of the reference lightLR, etc.

Herein, the reference-mirror driving mechanism 243 functions as oneexample of the “driver” of the present invention. Moreover, thecontroller 210 functions as one example of the “controller” of thepresent invention.

Furthermore, the controller 210 performs control for causing the display240A of the user interface (UI) 240 to display two kinds of imagesphotographed by the fundus oculi observation device 1: that is, a2-dimensional image of the surface of the fundus oculi Ef obtained bythe retinal camera unit 1A, and a tomographic image of the fundus oculiEf formed based on the detection signals obtained by the OCT unit 150.These images may be displayed on the display 240A separately, or may bedisplayed side by side simultaneously.

(Image Forming Part)

An image forming part 220 performs a process of forming image data ofthe fundus oculi image based on the video signals from the imagingdevices 10 and 12 of the retinal camera unit 1A, and a process offorming image data of the tomographic images of the fundus oculi Efbased on the detection signals from the CCD 184 of the OCT unit 150.

In particular, in the image-forming process based on the detectionsignals from the OCT unit 150, the image forming part 220 forms atomographic image within a predetermined frame. Herein, the frame refersto a frame that becomes the range of formation of an image. At the timeof displaying an image, an image formed within the frame is to bedisplayed.

When the retinal camera unit 1A is moved in the x-direction ory-direction, an image formed within the frame changes in the surfacedirection of the fundus oculi Ef. Furthermore, when the reference mirror174 is moved, namely, when the optical path length of the referencelight LR is changed, the depth position of an image formed within theframe changes. Thus, by appropriately aligning the position of theretinal camera unit 1A or the position of the reference mirror 174, itis possible to form an image of the fundus oculi Ef at a desiredposition and depth within the frame.

The imaging forming part 220 comprises the imaging forming board 208 andthe communication interface 209. In this specification, “image” may beidentified with “image data” corresponding thereto.

Herein, the image forming part 220 (OCT-image forming board 208 b)functions as one example of the “image forming part” of the presentinvention.

(Image Processor)

The image processor 230 applies various image processing and analysisprocess to image data of images formed by the image forming part 220.For example, the image processor 230 executes a process of forming imagedata of a 3-dimensional image of the fundus oculi Ef based on thetomographic images corresponding to the detection signal from the OCTunit 150, and various correction processes such as brightness correctionand dispersion correction of the images.

Herein, image data of a 3-dimensional image is image data made byassigning pixel values to each of a plurality of voxels arranged3-dimensionally, and is referred to as volume data, voxel data, and thelike. When displaying an image based on volume data, the image processor230 operates to apply a rendering process (such as volume rendering andMIP (Maximum Intensity Projection)) to this volume data and form imagedata of a pseudo 3-dimensional image seen from a specified viewingdirection. On a display device such as the display 207, the pseudo3-dimensional image based on the image data is displayed.

Furthermore, an analyzing part 231 is disposed to the image processor230. The analyzing part 231 conducts analytical processes for alignmentof a measurement position in the depth direction of the fundus oculi Efand functions as an example of the “analyzer” in the present invention.The analyzing part 231 includes a signal-level calculator 232, asignal-level determining part 233, an image-position specifying part234, and a movement-distance calculator 235. Hereinafter, each of theseparts 232 through 235 will be described.

(Signal-Level Calculator)

The signal-level calculator 232 analyzes an image (OCT image) formed bythe OCT-image forming board 208 b of the image forming part 220 andcalculates the signal level of the OCT image. As for the method ofcalculating the signal level of the image, it is possible to use anyknown method. The OCT image to become the subject for calculation of thesignal level may be a 2-dimensional tomographic image, or may be a1-dimensional image of the depth direction (to be described later).Herein, the signal level refers to the intensity of signal componentsincluded in the image data of an OCT image, and is the intensity of acomponent obtained after (at least part of) a noise component is removedfrom the image data of the OCT image. This signal component is acomponent in which morphology of the fundus oculi Ef has been reflected.

(Signal-Level Determining Part)

The signal-level determining part 233 determines the size relation bycomparing the signal level value calculated by the signal-levelcalculator 232 with a predetermined threshold value. The threshold valueis previously set and stored in a hard disk drive 204 a or the like.

(Image-Position Specifying Part)

The image-position specifying part 234 analyzes the OCT image whosesignal level is determined to be over the threshold value by thesignal-level determining part 233, and finds the position of thepredetermined partial image in the frame previously described. Thispartial image is, for example, an image corresponding to a predetermineddepth position of the fundus oculi Ef. As the depth position, forexample, of a plurality of layers composing the fundus oculi Ef (nervefiber layer, photoreceptor layer, retinal pigment epithelium, etc.), alayer in which the pixel value (brightness value or the like) within theOCT image becomes the greatest.

The partial image specified by the image-position specifying part 234 isnot limited to those described above but may also be an image equivalentto any layer among the plurality of layers composing the fundus oculiEf. Moreover, it is possible to specify an image region equivalent tothe surface of the fundus oculi Ef as the partial region describedabove.

(Movement-Distance Calculator)

The movement-distance calculator 235 calculates the distance of movementof the reference mirror 174 based on the position of the partial imagespecified by the image-position specifying part 234.

To explain more concretely, first, the movement-distance calculator 235calculates the displacement between the position of a partial imagewithin the frame obtained by the image-position specifying part 234 anda specific position within the frame. This specific position ispreviously set as the predetermined depth position within the frame.Furthermore, this specific position is set at a position within a framewhere the measurement sensitivity in measurement for capturing an OCTimage is relatively favorable.

Assuming a coordinate value of the depth direction (z-direction) of thespecific position within the frame is z0 and a coordinate value of thespecific position of the partial image is z, the movement-distancecalculator 235 calculates displacement Δz=z−z0. This method iseffective, for example, when the partial image is a 1-dimensional imageor when the z coordinate values of the respective pixels composing a2-dimensional partial image are the same.

On one hand, in a case in which the partial image is a 2-dimensionalimage and also includes a pixel of different z coordinate value, it isdifficult to employ the above method. Moreover, in a case in which thepartial image includes a plurality of 1-dimensional images, it is alsodifficult to employ the above method. Then, in these cases, for example,the displacement Δz can be found by employing a method as follows.

First, a z coordinate value z1 of a specified pixel of the specifiedpartial image is found, and this z coordinate value z1 is assumed to bea z coordinate value of the partial image. Then, z1−z0 is calculated,and the result of this calculation is assumed to be the displacement Δz.Herein, as the above-described specified pixel, for example, a pixelwith the maximum or minimum z coordinate value, a pixel with a medium zcoordinate value (in the middle of the maximum and the minimum), and apixel that becomes a center in a direction orthogonal to a depthdirection may be used.

Another method may be to define the average value of the z coordinatevalues of a plurality of pixels composing a partial image as a zcoordinate value of the partial image. For example, in a case in which apartial image composed of a plurality of 1-dimensional images (images ofthe depth direction to be described later) is taken into consideration,a pixel with the maximum pixel value is specified in each of the1-dimensional images, and the average value of the z coordinate valuesof the specified plurality of pixels can be defined as a z coordinatevalue of the partial image.

After the displacement Δz is calculated as described above, themovement-distance calculator 235 calculates the movement distance of thereference mirror 174 corresponding to this displacement Δz. The distanceof z-direction within a frame is previously associated with the distanceof the depth direction (z-direction) of the fundus oculi Ef. Themovement-distance calculator 235 calculates the distance of the depthdirection of the fundus oculi Ef that corresponds to the displacement Δzwithin the frame, based on the association of the distances. In anoptical image measurement device, an image of the fundus oculi Ef iscaptured at the almost the same depth position as the optical distancefrom the optical coupler 162 to the reference mirror 174. Therefore, themovement distance of the reference mirror 174 becomes equal to thedistance of the depth direction of the fundus oculi Ef calculated by themovement-distance calculator 235.

The image processor 230 that operates as described above comprises themicroprocessor 201, the RAM 202, the ROM 203, and the hard disk drive204 (control program 204 a).

(User Interface)

The user interface (UI) 240 comprises the display 240A and an operationpart 240B. The display 240A is composed of a display device such as thedisplay 207. Further, the operation part 240B is composed of an inputdevice or an operation device such as the keyboard 205 and the mouse206.

(Operation Panel)

The operation panel 3 a of the retinal camera unit 1A will be described.

The operation panel 3 a is arranged on the platform 3 of the retinalcamera unit 1A, for example.

The operation panel 3 a is provided with an operating part used toinstruct an operation for capturing a 2-dimensional image of the surfaceof the fundus oculi Ef, and an operating part used to instruct anoperation for capturing a tomographic image of the fundus oculi Ef.

Placement of the operation panel 3 a makes it possible to execute anoperation for capturing a fundus oculi image Ef and an operation forcapturing a tomographic image in the same manner as when operating aconventional retinal camera.

As shown in FIG. 6, the operation panel 3 a is provided with, forexample, a menu switch 301, a split switch 302, an imaging light amountswitch 303, an observation light amount switch 304, a jaw holder switch305, a photographing switch 306, a zoom switch 307, an image switchingswitch 308, a fixation target switching switch 309, a fixation targetposition adjusting switch 310, a fixation target size switching switch311, and a mode switching knob 312.

The menu switch 301 is a switch operated to display a certain menuscreen for a user to select and designate various menus (such as animaging menu for imaging a 2-dimensional image of the surface of thefundus oculi Ef, a tomographic image and the like, and a setting menufor inputting various settings).

When this menu switch 301 is operated, the operation signal is inputtedto the controller 210. The controller 210 causes the touch panel monitor11 or the display 240A to display a menu screen, in response to theinput of the operation signal. A controller (not shown) may be providedin the retinal camera unit 1A, whereby the controller causes the touchpanel monitor 11 to display the menu screen.

The split switch 302 is a switch operated to switch the light on and offof the split bright line for focusing (e.g., see JP Patent laid-open No.H9-66031. Also referred to as split target, split mark and so on.). Theconfiguration for projecting this split bright line onto the eye E(split bright line projection part) is housed, for example, in theretinal camera unit 1A (not shown in FIG. 1).

When this split switch 302 is operated, the operation signal is inputtedto the controller 210 (or the aforementioned controller inside theretinal camera unit 1A; the same hereinafter). The controller 210projects the split bright line onto the eye E by controlling the splitbright line projection part, in response to the input of this operationsignal.

The imaging light amount switch 303 is a switch operated to adjust theemitted light amount of the imaging light source 103 (photographinglight amount) depending on the state of the eye E (such as the degree ofopacity of the lens). This imaging light amount switch 303 is providedwith, for example, a photographing light amount increasing switch “+”for increasing the photographing light amount, a photographing lightamount decreasing switch “−” for decreasing the photographing lightamount, and a reset switch (a button in the middle) for setting thephotographing light amount to a predetermined initial value (defaultvalue).

When one of the imaging light amount switches 303 is operated, theoperation signal is inputted to the controller 210. The controller 210controls the imaging light source 103 in response to the inputtedoperation signal and adjusts the photographing light amount.

The observation light amount switch 304 is a switch operated to adjustthe emitted light amount (observation light amount) of the observationlight source 101. The observation light amount switch 304 is providedwith, for example, an observation light amount increasing switch “+” forincreasing the observation light amount, and an observation light amountdecreasing switch “−” for decreasing the observation light amount.

When one of the observation light amount switches 304 is operated, theoperation signal is inputted to the controller 210. The controller 210controls the observation light source 101 in response to the inputtedoperation signal and adjusts the observation light amount.

The jaw holder switch 305 is a switch to move the position of the jawholder (not shown) of the retinal camera unit 1A. This jaw holder switch305 is provided with, for example, an upward movement switch (upwardtriangle) for moving the jaw holder upward, and a downward movementswitch (downward triangle) for moving the jaw holder downward.

When one of the jaw holder switches 305 is operated, the operationsignal is inputted to the controller 210. The controller 210 controls ajaw holder movement mechanism (not shown) in response to the inputtedoperation signal and moves the jaw holder upward or downward.

The photographing switch 306 is a switch used as a trigger switch forcapturing a 2-dimensional image of the surface of the fundus oculi Ef ora tomographic image of the fundus oculi Ef.

When the photographing switch 306 is operated in a state where a menu tophotograph a 2-dimensional image is selected, the controller 210 thathas received the operation signal controls the imaging light source 103to emit photographing illumination light, and also causes the display240A or the touch panel monitor 11 to display a 2-dimensional image ofthe surface of the fundus oculi Ef, based on the video signal outputtedfrom the imaging device 10 having detected the fundus oculi reflectionlight.

On the other hand, when the photographing switch 306 is operated in astate where a menu to capture a tomographic image is selected, thecontroller 210 that has received the operation signal controls thelow-coherence light source 160 to emit the low-coherence light L0, andalso controls the Galvano mirrors 141A and 141B to scan the signal lightLS. Moreover, the controller 210 causes the display 240A or the touchpanel monitor 11 to display a tomographic image of the fundus oculi Efformed by the image forming part 220 (and image processor 230), based onthe detection signal outputted from the CCD 184 that has detected theinterference light LC.

The zoom switch 307 is a switch operated to change the angle of view(zoom magnification) at the time of photographing of the fundus oculiEf. Every time this zoom switch 307 is operated, the photographing angleis set alternately to 45 degrees and 22.5 degrees, for example.

When this zoom switch 307 is operated, the controller 210 that hasreceived the operation signal controls a variable magnifying lensdriving mechanism (not shown) to move the variable magnifying lens 124in the optical axis direction of the imaging optical system 120, therebychanging the photographing angle of view.

The image switching switch 308 is a switch operated to switch displayedimages. When the image switching switch 308 is operated in a state wherea fundus oculi observation image (a 2-dimensional image of the surfaceof the fundus oculi Ef based on the video signal from the imaging device12) is displayed on the display 240A or the touch panel monitor 11, thecontroller 210 having received the operation signal controls the display240A or touch panel monitor 11 to display the tomographic image of thefundus oculi Ef.

On the other hand, when the image switching switch 308 is operated in astate where a tomographic image of the fundus oculi is displayed on thedisplay 240A or the touch pane monitor 11, the controller 210 havingreceived the operation signal controls the display 240A or the touchpanel monitor 11 to display the fundus oculi observation image.

The fixation target switching switch 309 is a switch operated to switchthe position of the internal fixation target displayed by the LCD 140(i.e. the projection position of the internal fixation target on thefundus oculi Ef). By operating this fixation target switching switch309, the display position of the internal fixation target can beswitched, for example, among “fixation position to capture the image ofthe peripheral region of the center of the fundus oculi (fixationposition for fundus oculi center imaging),” “fixation position tocapture the image of the peripheral region of macula lutea (fixationposition for macula lutea imaging)” and “fixation position to capturethe image of the peripheral region of papilla (fixation position forpapilla imaging),” in a circulative fashion.

In response to the operation signals from the fixation target switchingswitch 309, the controller 210 causes the LCD 140 to display theinternal fixation target in different positions on the display surfacethereof. The display positions of the internal fixation targetcorresponding to the above three fixation positions, for example, can bepreset based on clinical data, or can be set for each eye or for eachimage photographing in advance.

The fixation target position adjusting switch 310 is a switch operatedto adjust the display position of the internal fixation target. Thisfixation target position adjusting switch 310 is provided with, forexample, an upward movement switch for moving the display position ofthe internal fixation target upward, a downward movement switch formoving it downward, a leftward movement switch for moving it leftward, arightward movement switch for moving it rightward, and a reset switchfor moving it to a predetermined initial position (default position).

Upon reception of the operation signal from either of these switches ofthe fixation target position adjusting switch 310, the controller 210controls the LCD 140 to move the display position of the internalfixation target, in response to the operation signal.

The fixation target size switching switch 311 is a switch operated tochange the size of the internal fixation target. When this fixationtarget size switching switch 311 is operated, the controller 210 thathas received the operation signal controls the LCD 140 to change thedisplay size of the internal fixation target. The display size of theinternal fixation target can be switched, for example, between “normalsize” and “enlarged size,” alternately. As a result, the size of theprojection image of the fixation target projected onto the fundus oculiEf is changed. Upon reception of the operation signal from the fixationtarget position adjusting switch 311, the controller 210 controls theLCD 140 to change the display size of the internal fixation target, inresponse to the operation signal.

The mode switching knob 312 is a knob rotationally operated to selectvarious photographing modes. The photographing modes are, for example, afundus oculi photographing mode to photograph a 2-dimensional image ofthe fundus oculi Ef, a B-scan mode to perform B-scan of the signal lightLS, and a 3-dimensional scan mode to scan with the signal light LS3-dimensionally. In addition, the mode switching knob 312 may beconfigured so as to be capable of selecting a replay mode to replay anddisplay a captured 2-dimensional image or tomographic image of thefundus oculi Ef. In addition, it may be configured so as to be capableof selecting a photographing mode to control so that the photographingof the fundus oculi Ef would be performed immediately after scanning ofthe signal light LS. Control of each part of the device for causing thefundus oculi observation device 1 to execute the operation correspondingto the each mode is executed by the controller 210.

Herein, the feature of control of scanning of the signal light LS by thecontroller 210, and the feature of processing to the detection signalfrom the OCT unit 150 by the image forming part 220 and the imageprocessor 230 will be respectively described. An explanation regardingthe process by the image forming part 220, etc., to the video signalfrom the retinal camera unit 1A will be omitted because it is the sameas the conventional process.

Signal Light Scanning

Scanning of the signal light LS is performed by changing the positions(directions of the reflecting surfaces) of the Galvano mirrors 141A and141B of the scan unit 141 in the retinal camera unit 1A. By controllingthe mirror drive mechanisms 241 and 242 respectively to change thedirections of the reflecting surfaces of the Galvano mirrors 141A and141B respectively, the controller 210 scans the application position ofthe signal light LS on the fundus oculi Ef.

When the facing direction of the reflecting surface of the Galvanomirror 141A is changed, the signal light LS is scanned in the horizontaldirection (x-direction in FIG. 1) on the fundus oculi Ef. Whereas, whenthe facing direction of the reflecting surface of the Galvano mirror141B is changed, the signal light LS is scanned in the verticaldirection (y-direction in FIG. 1) on the fundus oculi Ef. Further, bychanging the facing directions of the reflecting surfaces of both theGalvano mirrors 141A and 141B simultaneously, it is possible to scan thesignal light LS in the composed direction of the x-direction andy-direction. That is, by controlling these two Galvano mirrors 141A and141B, it is possible to scan the signal light LS in any direction on thex-y plane.

FIGS. 8A and 8B shows one example of the feature of scanning of thesignal light LS for forming images of the fundus oculi. Ef. FIG. 8Ashows one example of the feature of scanning of the signal light LS,when the fundus oculi Ef is seen from a direction that the signal lightLS enters the eye E (that is, seen from −z side toward +z side in FIG.1). Further, FIG. 8B shows one example of the feature of arrangement ofscanning points (positions at which image measurement is carried out;target positions of the signal light LS) on each scanning line on thefundus oculi Ef.

As shown in FIG. 8A, the signal light LS is scanned within arectangular-shaped scanning region R that has been preset. Within thisscanning region R, a plurality of (m number of) scanning lines R1through Rm are set in the x-direction. When the signal light LS isscanned along the respective scanning lines Ri (i=1 through m),detection signals of the interference light LC are generated.

Herein, a direction of each scanning line Ri will be referred to as the“main scanning direction” and a direction orthogonal thereto will bereferred to as the “sub-scanning direction”. Accordingly, scanning ofthe signal light LS in the main scanning direction is performed bychanging the facing direction of the reflecting surface of the Galvanomirror 141A, and scanning in the sub-scanning direction is performed bychanging the facing direction of the reflecting surface of the Galvanomirror 141B.

On each scanning line Ri, as shown in FIG. 8B, a plurality of (n numberof) scanning points Ril through Rin are preset.

In order to execute the scanning shown in FIGS. 8A and 8B, thecontroller 210 firstly controls the Galvano mirrors 141A and 141B to setthe target of the signal light LS entering into the fundus oculi Ef to ascan start position RS (scanning point R11) on the first scanning lineR1. Subsequently, the controller 210 controls the low-coherence lightsource 160 to flush the low-coherence light L0, thereby making thesignal light LS enter the scan start position RS. The CCD 184 receivesthe interference light LC based on the fundus oculi reflection light ofthis signal light LS at the scan start position RS, and outputs thedetection signal to the controller 210.

Next, the controller 210 controls the Galvano mirror 141A to scan thesignal light LS in the main scanning direction and set the incidenttarget of the signal light LS to a scanning point R12, and makes thelow-coherence light L0 flushed to make the signal light LS enter intothe scanning point R12. The CCD 184 receives the interference light LCbased on the fundus oculi reflection light of this signal light LS atthe scanning point R12, and then outputs the detection signal to thecontroller 210.

Likewise, the controller 210 obtains detection signals outputted fromthe CCD 184 in response to the interference light LC for each scanningpoint, by flushing the low-coherence light L0 at each scanning pointwhile shifting the incident target of the signal light LS from scanningpoint R13 to R14, ----, R1 (n−1), and R1 n in order.

Once the measurement at the last scanning point R1 n of the firstscanning line R1 is finished, the controller 210 controls the Galvanomirrors 141A and 141B simultaneously to shift the incident target of thesignal light LS to the first scanning point R21 of the second scanningline R2 following a line switching scan r. Then, by conducting thepreviously described measurement on each scanning point R2 j (j=1through n) of this second scanning line R2, detection signalscorresponding to the respective scanning points R2 j are obtained.

Likewise, the measurement is conducted for each of the third scanningline R3, ----, the m−1th scanning line R(m−1), the mth scanning line Rmto obtain the detection signals corresponding to the respective scanningpoints. Symbol RE on a scanning line Rm is a scan end positioncorresponding to a scanning point Rmn.

As a result, the controller 210 obtains m×n number of detection signalscorresponding to m×n number of scanning points Rij (i=1 through m, j=1through n) within the scanning region R. Hereinafter, a detection signalcorresponding to the scanning point Rij may be represented by Dij.

Such interlocking control of the shift of scanning points and theemission of the low-coherence light L0 can be realized by synchronizing,for instance, timing for transmission of control signals to the mirrordrive mechanisms 241 and 242 and timing for transmission of controlsignals (output request signals) to the low-coherence light source 160.

As described above, when each of the Galvano mirrors 141A and 141 B isoperated, the controller 210 stores the position of each scanning lineRi and the position of each scanning point Rij (coordinates on the x-ycoordinate system) as information representing the content of theoperation. This stored content (scanning point coordinate information)is used in an image forming process as in conventional one.

Image Processing

Next, one example of a process on OCT images (tomography images of thefundus oculi Ef) by the image forming part 220 and the image processor230 will be described.

The image forming part 220 executes the formation process of tomographicimages of the fundus oculi Ef along each scanning line Ri (main scanningdirection). Further, the image processor 230 executes the formationprocess of a 3-dimensional image of the fundus oculi Ef based on thesetomographic images formed by the image forming part 220, etc.

The formation process of a tomographic image by the image forming part220, as in the conventionally one, includes a 2-step arithmetic process.In the first step of the arithmetic process, based on a detection signalDij corresponding to each scanning point Rij, an image in the depth-wisedirection (z-direction in FIG. 1) of the fundus oculi Ef at the scanningpoint Rij is formed.

FIG. 9 shows a feature of (a group of) tomographic images formed by theimage forming part 220. In the second step of the arithmetic process, oneach scanning line Ri, based on the images in the depth-wise directionat the n number of scanning points Ril through Rin, a tomographic imageGi of the fundus oculi Ef along the scanning line Ri is formed. Then,the image forming part 220 determines the arrangement and the distanceof the scanning points Ril through Rin referring to the positionalinformation (scanning point coordinate information described before) ofthe scanning points Ril through Rin, and forms a tomographic image Gialong this scanning line Ri.

Through the above process, m number of tomographic images (a group oftomographic images) G1 through Gm at different positions in thesub-scanning direction (y-direction) are obtained.

Next, the formation process of a 3-dimensional image of the fundus oculiEf by the image processor 230 will be explained. A 3-dimensional imageof the fundus oculi Ef is formed based on the m number of tomographicimages obtained through the above arithmetic process. The imageprocessor 230 forms a 3-dimensional image of the fundus oculi Ef byperforming a known interpolating process to interpolate an image betweenthe adjacent tomographic images Gi and G (i+1).

Here, the image processor 230 determines the arrangement and distance ofeach scanning line Ri while referring to the positional information ofeach scanning line Ri to form this 3-dimensional image. For this3-dimensional image, a 3-dimensional coordinate system (x,y,z) is set,based on the positional information (the scanning point coordinateinformation) of each scanning point Rij and the z-coordinate in thedepth-wise image.

Furthermore, based on this 3-dimensional image, the image processor 230can form a tomographic image of the fundus oculi Ef at a cross-sectionin any direction other than the main scanning direction (x-direction).Once the cross-section is designated, the image processor 230 determinesthe position of each scanning point (and/or an interpolated depth-wiseimage) on this designated cross-section, and extracts a depth-wise imageat each determined position (and/or an interpolated depth-wise image),thereby forming a tomographic image of the fundus oculi Ef at thedesignated cross-section by arranging plural extracted depth-wiseimages.

Furthermore, an image Gmj shown in FIG. 9 represents an image in thedepth-wise direction (z-direction) at the scanning point Rmj on thescanning line Rm. A depth-wise image at each scanning point Rij on thescanning line Ri formed by the first-step arithmetic process isrepresented as “image Gij.”

[Usage Pattern]

A usage pattern of the fundus oculi observation device 1 having theconfiguration as described above will be explained. A flowchart shown inFIG. 10 shows one example of the usage pattern of the fundus oculiobservation device 1. The usage pattern shown in this flowchart is forautomation of alignment of the measurement position in the depthdirection of the fundus oculi Ef.

(Step 1)

First, the controller 210 controls the reference mirror drivingmechanism 243 to place the reference mirror 174 at the predeterminedinitial position (S1). This initial position is previously set. In thisembodiment, the reference mirror 174 is moved to a position where theoptical path length of the reference light LR becomes the shortest. Inother words, the reference mirror 174 is placed in the position closestto the optical coupler 162 within the movable range of the referencemirror 174.

(Step 2)

Next, measurement for capturing an OCT image is performed (S2). Aspecific example of this process will be described below. First, thecontroller 210 controls the low-coherence light source 160 to output thelow-coherence light L0, and also controls the mirror driving mechanisms241 and 242 to scan with the signal light LS. The reference light LRpassed through the reference mirror 174 and the signal light LS passedthrough the fundus oculi Ef are superimposed by the optical coupler 162,whereby the interference light LC is generated. The interference lightLC is split by the diffraction grating 182, and each spectrum isdetected by the CCD184. The CCD 184 transmits detection signals to thearithmetic control unit 200. This process is performed with respect toone scanning line Ri, for example (i.e., this process is performed withrespect to n number of scanning points R11 to Rin).

(Step 3)

Subsequently, the image forming part 220 forms an OCT image based on thedetection signals inputted from the CCD 184 (S3). At this time, it ispossible to shorten the processing time by performing a process asdescribed below, for example.

First, the image forming part 220 takes out detection signals at apredetermined number of scanning points from the n number of detectionsignals inputted from the CCD 184. The number of the detection signalsto be taken out is determined beforehand, for example, to beapproximately ten.

Furthermore, the image forming part 220 forms an image Gij (OCT image)of the depth direction based on the respective detection signals havingbeen taken out. Consequently, the predetermined number of images of thedepth direction can be captured.

(Step 4)

Next, the signal-level calculator 232 calculates the signal level of theOCT image formed by the image forming part 220 (S4). Then, thesignal-level calculator 232 calculates, for example, the signal level ofthe image of each depth direction formed in Step 3.

(Step 5)

Next, the signal-level determining part 233 determines whether thesignal level calculated by the signal-level calculator 232 exceeds athreshold value (S5). Then, the signal-level determining part 233determines, for example, whether the signal level of an image of eachdepth direction calculated in Step 4 exceeds the threshold value, anddetermines as “Y” when the signal levels of all the depth images exceedthe threshold value. The determination as “Y” may also be made when apredetermined number of signal levels exceed the threshold value among aplurality of images of the depth direction.

Herein, the fact that the signal level exceeds the threshold value isequivalent to the fact that a tomographic image of the fundus oculi Efis included within a frame of the OCT image. On one hand, the fact thatthe signal level is equal to or less than the threshold value means thatthe image of the fundus oculi Ef is not included within the frame of theOCT image. Even in a case in which the tomographic image of the fundusoculi Ef is included within the frame of the OCT image, it is not clearat this stage whether this tomographic image is placed in a favorableposition (e.g., a position with favorable measurement sensitivity)within the frame.

(Step 6)

When it is determined that the signal level is equal to or less than thethreshold value in Step 5 (S5; N), the controller 210 controls thereference mirror driving mechanism 243 to move the reference mirror 174by a specified distance (S6). The specified distance is set in advance.

In this embodiment, the position where the optical path length of thereference light LR becomes the shortest is the initial position of thereference mirror 174 (refer to Step 1), and therefore, the referencemirror 174 is moved in a manner that the optical path length of thereference mirror LR is longer by the specified distance.

When the reference mirror 174 is moved by the specified distance, theprocessing returns to S2, and the process up to Step 5 is executedagain. Thus, until the result of determination at Step 5 becomes “Y,”the process from Step 2 through Step 5 is repeated. In other words,until a tomographic image of the fundus oculi Ef shows up within theframe of the OCT image, such an action is made to gradually change theoptical path length of the reference light LR by a specified distance.

(Step 7)

In a case where it is determined in Step 5 that the signal level exceedsthe threshold value (S5; Y), the image-position specifying part 234specifies the position within the frame of a predetermined partial imageof each OCT image (S7).

(Step 8)

Subsequently, the movement-distance calculator 235 calculates thedistance of movement of the reference mirror 174, based on the positionwithin the frame of the partial image specified in Step 7 (S8).

(Step 9)

The controller 210 moves the reference mirror 174 by the movementdistance calculated in Step 8 (S9). Thus, the depth position of thefundus oculi Ef equivalent to the partial image and the specificposition within the frame coincide.

(Step 10)

When the movement of the reference mirror 174 in Step 9 is complete, thecontroller 210 controls the low-coherence light source 160, the mirrordriving mechanisms 241, 242, and so on to measure the OCT image(tomographic image) of the fundus oculi Ef (S10). The process from Step1 through Step 9 is preparation for capturing the OCT image of thefundus oculi Ef, and Step 10 is actual measurement of the OCT image. Theexplanation of the usage pattern related to this embodiment ends here.

Specific Example

A specific example of the usage pattern of the fundus oculi observationdevice 1 described thus far will be described with reference to FIG. 11through FIG. 13.

When an OCT image is captured in a case where the determination resultin Step 5 of the above usage pattern is “N,” an OCT image H1 as shown inFIG. 11 is acquired. The OCT image H1 is formed within a frame F, but atomographic image of the fundus oculi Ef is not included within theframe F. In this case, since the depth position corresponding to theposition of the reference mirror 174 exists within the vitreous body,the tomographic image of the fundus oculi Ef does not show up within theframe F.

Reference symbol F0 in FIG. 11 denotes a specific position within theframe F described in the process for calculating the movement distanceof the reference mirror 174. In the frame F shown in FIG. 11,measurement sensitivity is favorable on the side with a smaller zcoordinate value (i.e., the upper side of the paper in FIG. 11). This isbecause the initial position of the reference mirror 174 corresponds tothe side with a smaller z coordinate value as described in Step 1.

When an OCT image is captured when the determination result in Step 5 is“Y,” an OCT image H2 as shown in FIG. 12 is acquired. This OCT image H2is formed within the frame F, and includes a tomographic image of thefundus oculi Ef in a region on a side where the z coordinate valuewithin the frame F is greater (i.e., lower side of the paper in FIG.12). Reference symbol h within FIG. 12 denotes a layer of the fundusoculi Ef equivalent to the above-described partial image with thegreatest pixel value.

The OCT image H2 shown in FIG. 12 includes the tomographic image of thefundus oculi Et but this tomographic image is displayed in a regionwithin the frame F where measurement sensitivity is not favorable. Inthe above usage pattern, a tomographic image is to be displayed in aregion within the frame F with favorable measurement sensitivity by theprocess from Step 7 through Step 9.

That is to say, the position within the frame F of a partial imageequivalent to the layer h of the OCT image H2 is specified in Step 7,and the movement distance of the reference mirror 174 is found in Step 8by calculating the displacement between the z coordinate value of thelayer h and the z coordinate value of the specific position F0. Then, inStep 9, the reference mirror 174 is moved by the movement distance.

By conducting such a process, a tomographic image of the fundus oculi Efis displayed in a manner that the layer h is placed in the specificposition F0 within the frame F, like an OCT image H3 shown in FIG. 13.As described above, the specific position F0 is set in a position withinthe frame F where the measurement sensitivity is favorable. Therefore,the tomographic image in the OCT image H3 is clearly displayed incomparison with the tomographic image within the OCT image H2 of FIG.12.

ACTIONS AND ADVANTAGEOUS EFFECTS

Actions and advantageous effects of the fundus oculi observation device1 as described above will be described below.

The fundus oculi observation device 1 acts as an optical imagemeasurement device capable of measuring an OCT image such as atomographic image of the fundus oculi Ef, or the like, and is configuredso as to calculate the signal level of the formed OCT image, determinewhether the signal level exceeds a threshold value, and change theposition of the reference mirror 174 so that the signal level isdetermined to exceed the threshold value.

Since the fundus oculi observation device 1 acts so as to change theposition of the reference mirror 174 so that the signal level of an OCTimage to be formed becomes greater than the threshold value, it ispossible to automatically capture such an OCT image that includes atomographic image of the fundus oculi Ef within a frame. Thus, accordingto the fundus oculi observation device 1, it is possible to easily alignthe measurement position in the depth direction of the fundus oculi Ef(measurement subject).

In particular, since the fundus oculi observation device 1 is configuredso as to search the position of the reference mirror 174 where thesignal level exceeds the threshold value by sequentially changing theoptical path length of the reference light LR by a specified distancefrom the initial position until the tomographic image of the fundusoculi Ef shows up within the frame, it is possible to securely find thefavorable measurement position in the depth direction of the fundusoculi Ef.

Furthermore, since the fundus oculi observation device 1 is configuredso as to change the position of the reference mirror 174 so that apredetermined, partial image of an image whose signal level isdetermined to exceed the threshold value is placed in a specificposition within the frame, it is possible to easily capture an OCT imagein which the tomographic image of the fundus oculi Ef is placed in thevicinity region of the specific position within the frame. By setting aposition with favorable measurement sensitivity as the specific positionwhen measuring an OCT image, it is possible to easily capture a cleartomographic image of the fundus oculi Ef.

The actions and advantageous effects described above are exerted when atomographic image of the fundus oculi Ef is not included within a frameat an initial stage. On one hand, when the tomographic image of thefundus oculi Ef is included within the frame, such as when a tomographicimage of the fundus oculi Ef is included within the frame of an OCTimage at an initial stage, the fundus oculi observation device 1 has thefollowing characteristics. That is to say, the fundus oculi observationdevice 1 functions to change the position of a reference mirror 174 sothat a partial image equivalent to a predetermined depth position of thefundus oculi Ef is placed in a specific position within the frame.According to such a fundus oculi observation device 1, an OCT image inwhich a tomographic image of the fundus oculi Ef is placed in thevicinity region of the specific position within a frame can be easilyacquired, so it is possible to easily align the measurement position inthe depth direction of the fundus oculi Ef.

In the present invention, a difference in optical path length between asignal light and a reference light is changed in a manner that thesignal level or the ratio of the signal level and the noise level of animage exceeds a threshold value, so that an image including an image ofa measurement subject can be automatically captured. Therefore,according to the present invention, it is possible to easily align themeasurement position in the depth direction of the measurement subject.

Further, in the present invention, the difference in optical path lengthbetween the signal light and the reference light is changed in a mannerthat a partial image corresponding to a predetermined depth position ofthe measurement subject is located in a specific position within aframe, so that an image in which an image of the measurement subject islocated in the vicinity region of the specific position within the framecan be automatically captured. Therefore, according to the presentinvention, it is possible to easily align the measurement position inthe depth direction of the measurement subject.

[Modification]

The configuration described above is merely a specific example forfavorably implementing the present invention. Therefore, it is possibleto properly make any modification within the scope and intent of thepresent invention.

For example, in the embodiment described above, the difference betweenthe light path of a signal light and the light path of a reference light(difference in optical path length) is changed by changing the positionof the reference mirror 174, but the method for changing the differencein optical path length is not limited to this. For instance, it ispossible to change the difference in optical path length by integrallymoving the retinal camera unit 1A and the OCT unit 150 with respect tothe eye E and changing the optical path length of the signal light LS.Furthermore, it is also possible to change the difference in opticalpath length by moving a measurement subject in a depth direction(z-direction). In general, as the “changer” in the present invention, itis possible to employ any constitution for changing the difference inoptical path length between the signal light and reference light.

Moreover, in the embodiment described above, a state where the opticalpath length of the reference light is shortest is assumed to be aninitial state and a state where the signal level exceeds the thresholdvalue is searched, but it is also possible to configure so that anystate such as a state where the light path length of the reference lightis the longest is assumed to be an initial state and a target state issearched.

Furthermore, in the embodiment described above, a state where the signallevel exceeds the threshold value is searched while gradually increasingthe optical path length of the reference light, but it is also possibleto configure so that the target state is searched while graduallydecreasing the optical path length of the reference light. Moreover, itis also possible to configure so as to pursue the target state byincreasing and decreasing the optical path length of the referencelight. In addition, instead of changing the optical path length of thereference light, it is also possible to configure so as to search thetarget state by gradually increasing (or decreasing) the optical pathlength of the signal light or pursue the target state by increasing anddecreasing the optical path length of the signal light.

Moreover, in the embodiment described above, the position of an image ofthe measurement subject within a frame is determined based on the signallevel of an OCT image, but it is also possible to configure so that theposition of the image is determined based on the ratio of signal leveland noise level (S/N ratio).

Calculation of the S/N ratio of an OCT image is conducted by ananalyzing part 231 (analyzer). Furthermore, it is possible to employ anyknown method as a method for calculating the S/N ratio. Moreover, theOCT image to be subjected to calculation of the S/N ratio may be a2-dimensional tomographic image, or may be a 1-dimensional image of adepth direction.

By thus considering the S/N ratio, it is possible to increase theaccuracy in determining the image position. In particular, it may bedesired to consider the S/N ratio, for example, when the amount of noisecontained in an OCT image is large or noise cannot be removedeffectively due to the state of the measurement subject or the device.

The fundus oculi observation device described in the above embodiment iscomprises an optical image measurement device of Fourier domain type,but it is also possible to apply the configuration of the presentinvention to an optical image measurement device of Time Domain type.The time domain type of optical image measurement device is describedin, for example, Japanese Unexamined Patent Application Publication2005-241464. Moreover, it is also possible to apply the configuration ofthe present invention to an optical image measurement device of anyother type such as a Swept Source type.

[Program]

A program configured to control the device according to the presentinvention will be explained hereunder. In the above embodiments, thecontrol program 204 a is equivalent to the program.

This program is a computer program for controlling an optical imagemeasurement device having: a light source for outputting a low-coherencelight; an interference-light generator for generating an interferencelight by splitting the outputted low-coherence light into a signal lightheading toward a measurement subject and a reference light headingtoward a reference object, and superimposing the signal light passedthrough the measurement subject and the reference light passed throughthe reference object; a changer for changing the difference in opticalpath length between the signal light and the reference light; a detectorfor detecting the interference light; and an image forming part forforming an image based on the detection result, whereby: the opticalimage forming device is caused to function as an analyzer that analyzesthe image formed by the image forming part, calculates a signal level orthe ratio of a signal level and a noise level of the image anddetermines whether the calculated signal level or ratio of the signallevel and the noise level exceeds a threshold value; and the opticalimage forming device is caused to function as a controller forcontrolling the changer and changes the difference in optical pathlength so that the analyzer determines that the signal level or theratio of the signal level and the noise level exceeds the thresholdvalue.

This program is configured so as to change the difference in opticalpath length between the signal light and the reference light so that thesignal level or the ratio of the signal level and the noise level of animage exceeds the threshold value, whereby it is possible toautomatically capture an image including the image of the measurementsubject. Thus, according to this program, it is possible to easily alignthe measurement position of the measurement subject in the depthdirection.

Furthermore, this program is a computer program for controlling anoptical image measurement device having: a light source for outputting alow-coherence light; an interference-light generator for generating aninterference-light by splitting the outputted low-coherence light into asignal light heading toward a measurement subject and a reference lightheading toward a reference object, and superimposing the signal lightpassed through the measurement subject and the reference light passedthrough the reference object; a changer for changing the difference inoptical path length between the signal light and the reference light; adetector for detecting the interference-light; and an image-forming partfor forming an image within a predetermined frame based on the detectionresults, whereby the optical image-forming device is caused to functionas a controller for controlling the changer and changing the differencein optical path length so that a partial image equivalent to apredetermined depth position of the measurement subject in the imageformed by the image forming part is placed in a specific position withinthe frame.

This program is configured so as to change the difference in opticalpath length between the signal light and the reference light so that thepartial image equivalent to the predetermined depth position of themeasurement subject is placed in the specific position within the frame,whereby an image in which an image of the measurement subject is placedin the vicinity region of the specific position within the frame can betaken out automatically. Thus, according to this program, it is possibleto easily align the measurement position in the depth direction of themeasurement subject.

This program can be stored in any recording medium readable by a driveof the computer. For example, a storing medium such as an optical disk,a magneto-optical disk (CD-ROM, DVD-ROM, DVD-ROM, MO, etc.) and amagnetic storing medium (hard disk, Floppy Disk™, ZIP, etc.) can beused. Moreover, it is also possible to store the program in a storagedevice such as a hard disk drive or a memory. Furthermore, it is alsopossible to transmit the program via a network such as the Internet anda LAN.

1-5. (canceled)
 6. An optical image measurement device comprising: alight source configured to emit a low-coherence light; aninterference-light generator configured to generate a interference lightby splitting the emitted low-coherence light into a signal light headingtoward a measurement subject and a reference light heading toward areference object, and superimposing the signal light passed through themeasurement subject and the reference light passed through the referenceobject; a changer configured to change a difference in optical pathlength between the signal light and the reference light; a detectorconfigured to detect the generated interference light; an image formingpart configured to form an image within a predetermined frame defined bya length in the depth-wise direction of the measurement object based onthe result of the detection by the detector; a determination partconfigured to determine a positional relation between a predetermineddepth position of the measurement subject in the formed image and aspecific position within the predetermined frame; and a controllerconfigured to control the changer to change the difference in opticalpath length so that a partial image corresponding to a predetermineddepth position of the measurement subject in the formed image is placedin a specific position within the predetermined frame based on thedetermined positional relation.
 7. The optical image measurement deviceaccording to claim 6, wherein: the reference object is a mirrorreflecting the reference light; and the changer includes a driver movingthe mirror in a traveling direction of the reference light.